1 2Linux UWB + Wireless USB + WiNET
3 4 (C) 2005-2006 Intel Corporation
5 Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
6 7 This program is free software; you can redistribute it and/or
8 modify it under the terms of the GNU General Public License version
9 2 as published by the Free Software Foundation.
10 11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15 16 You should have received a copy of the GNU General Public License
17 along with this program; if not, write to the Free Software
18 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
19 02110-1301, USA.
20 21 22Please visit http://bughost.org/thewiki/Design-overview.txt-1.8 for
23updated content.
24 25 * Design-overview.txt-1.8
26 27This code implements a Ultra Wide Band stack for Linux, as well as
28drivers for the the USB based UWB radio controllers defined in the
29Wireless USB 1.0 specification (including Wireless USB host controller
30and an Intel WiNET controller).
31 32 1. Introduction
33 1. HWA: Host Wire adapters, your Wireless USB dongle
34 35 2. DWA: Device Wired Adaptor, a Wireless USB hub for wired
36 devices
37 3. WHCI: Wireless Host Controller Interface, the PCI WUSB host
38 adapter
39 2. The UWB stack
40 1. Devices and hosts: the basic structure
41 42 2. Host Controller life cycle
43 44 3. On the air: beacons and enumerating the radio neighborhood
45 46 4. Device lists
47 5. Bandwidth allocation
48 49 3. Wireless USB Host Controller drivers
50 51 4. Glossary
52 53 54 Introduction
55 56UWB is a wide-band communication protocol that is to serve also as the
57low-level protocol for others (much like TCP sits on IP). Currently
58these others are Wireless USB and TCP/IP, but seems Bluetooth and
59Firewire/1394 are coming along.
60 61UWB uses a band from roughly 3 to 10 GHz, transmitting at a max of
62~-41dB (or 0.074 uW/MHz--geography specific data is still being
63negotiated w/ regulators, so watch for changes). That band is divided in
64a bunch of ~1.5 GHz wide channels (or band groups) composed of three
65subbands/subchannels (528 MHz each). Each channel is independent of each
66other, so you could consider them different "busses". Initially this
67driver considers them all a single one.
68 69Radio time is divided in 65536 us long /superframes/, each one divided
70in 256 256us long /MASs/ (Media Allocation Slots), which are the basic
71time/media allocation units for transferring data. At the beginning of
72each superframe there is a Beacon Period (BP), where every device
73transmit its beacon on a single MAS. The length of the BP depends on how
74many devices are present and the length of their beacons.
75 76Devices have a MAC (fixed, 48 bit address) and a device (changeable, 16
77bit address) and send periodic beacons to advertise themselves and pass
78info on what they are and do. They advertise their capabilities and a
79bunch of other stuff.
80 81The different logical parts of this driver are:
82 83 *
84 85 *UWB*: the Ultra-Wide-Band stack -- manages the radio and
86 associated spectrum to allow for devices sharing it. Allows to
87 control bandwidth assignment, beaconing, scanning, etc
88 89 *
90 91 *WUSB*: the layer that sits on top of UWB to provide Wireless USB.
92 The Wireless USB spec defines means to control a UWB radio and to
93 do the actual WUSB.
94 95 96 HWA: Host Wire adapters, your Wireless USB dongle
97 98WUSB also defines a device called a Host Wire Adaptor (HWA), which in
99mere terms is a USB dongle that enables your PC to have UWB and Wireless
100USB. The Wireless USB Host Controller in a HWA looks to the host like a
101[Wireless] USB controller connected via USB (!)
102 103The HWA itself is broken in two or three main interfaces:
104 105 *
106 107 *RC*: Radio control -- this implements an interface to the
108 Ultra-Wide-Band radio controller. The driver for this implements a
109 USB-based UWB Radio Controller to the UWB stack.
110 111 *
112 113 *HC*: the wireless USB host controller. It looks like a USB host
114 whose root port is the radio and the WUSB devices connect to it.
115 To the system it looks like a separate USB host. The driver (will)
116 implement a USB host controller (similar to UHCI, OHCI or EHCI)
117 for which the root hub is the radio...To reiterate: it is a USB
118 controller that is connected via USB instead of PCI.
119 120 *
121 122 *WINET*: some HW provide a WiNET interface (IP over UWB). This
123 package provides a driver for it (it looks like a network
124 interface, winetX). The driver detects when there is a link up for
125 their type and kick into gear.
126 127 128 DWA: Device Wired Adaptor, a Wireless USB hub for wired devices
129 130These are the complement to HWAs. They are a USB host for connecting
131wired devices, but it is connected to your PC connected via Wireless
132USB. To the system it looks like yet another USB host. To the untrained
133eye, it looks like a hub that connects upstream wirelessly.
134 135We still offer no support for this; however, it should share a lot of
136code with the HWA-RC driver; there is a bunch of factorization work that
137has been done to support that in upcoming releases.
138 139 140 WHCI: Wireless Host Controller Interface, the PCI WUSB host adapter
141 142This is your usual PCI device that implements WHCI. Similar in concept
143to EHCI, it allows your wireless USB devices (including DWAs) to connect
144to your host via a PCI interface. As in the case of the HWA, it has a
145Radio Control interface and the WUSB Host Controller interface per se.
146 147There is still no driver support for this, but will be in upcoming
148releases.
149 150 151 The UWB stack
152 153The main mission of the UWB stack is to keep a tally of which devices
154are in radio proximity to allow drivers to connect to them. As well, it
155provides an API for controlling the local radio controllers (RCs from
156now on), such as to start/stop beaconing, scan, allocate bandwidth, etc.
157 158 159 Devices and hosts: the basic structure
160 161The main building block here is the UWB device (struct uwb_dev). For
162each device that pops up in radio presence (ie: the UWB host receives a
163beacon from it) you get a struct uwb_dev that will show up in
164/sys/class/uwb and in /sys/bus/uwb/devices.
165 166For each RC that is detected, a new struct uwb_rc is created. In turn, a
167RC is also a device, so they also show in /sys/class/uwb and
168/sys/bus/uwb/devices, but at the same time, only radio controllers show
169up in /sys/class/uwb_rc.
170 171 *
172 173 [*] The reason for RCs being also devices is that not only we can
174 see them while enumerating the system device tree, but also on the
175 radio (their beacons and stuff), so the handling has to be
176 likewise to that of a device.
177 178Each RC driver is implemented by a separate driver that plugs into the
179interface that the UWB stack provides through a struct uwb_rc_ops. The
180spec creators have been nice enough to make the message format the same
181for HWA and WHCI RCs, so the driver is really a very thin transport that
182moves the requests from the UWB API to the device [/uwb_rc_ops->cmd()/]
183and sends the replies and notifications back to the API
184[/uwb_rc_neh_grok()/]. Notifications are handled to the UWB daemon, that
185is chartered, among other things, to keep the tab of how the UWB radio
186neighborhood looks, creating and destroying devices as they show up or
187disappear.
188 189Command execution is very simple: a command block is sent and a event
190block or reply is expected back. For sending/receiving command/events, a
191handle called /neh/ (Notification/Event Handle) is opened with
192/uwb_rc_neh_open()/.
193 194The HWA-RC (USB dongle) driver (drivers/uwb/hwa-rc.c) does this job for
195the USB connected HWA. Eventually, drivers/whci-rc.c will do the same
196for the PCI connected WHCI controller.
197 198 199 Host Controller life cycle
200 201So let's say we connect a dongle to the system: it is detected and
202firmware uploaded if needed [for Intel's i1480
203/drivers/uwb/ptc/usb.c:ptc_usb_probe()/] and then it is reenumerated.
204Now we have a real HWA device connected and
205/drivers/uwb/hwa-rc.c:hwarc_probe()/ picks it up, that will set up the
206Wire-Adaptor environment and then suck it into the UWB stack's vision of
207the world [/drivers/uwb/lc-rc.c:uwb_rc_add()/].
208 209 *
210 211 [*] The stack should put a new RC to scan for devices
212 [/uwb_rc_scan()/] so it finds what's available around and tries to
213 connect to them, but this is policy stuff and should be driven
214 from user space. As of now, the operator is expected to do it
215 manually; see the release notes for documentation on the procedure.
216 217When a dongle is disconnected, /drivers/uwb/hwa-rc.c:hwarc_disconnect()/
218takes time of tearing everything down safely (or not...).
219 220 221 On the air: beacons and enumerating the radio neighborhood
222 223So assuming we have devices and we have agreed for a channel to connect
224on (let's say 9), we put the new RC to beacon:
225 226 *
227 228 $ echo 9 0 > /sys/class/uwb_rc/uwb0/beacon
229 230Now it is visible. If there were other devices in the same radio channel
231and beacon group (that's what the zero is for), the dongle's radio
232control interface will send beacon notifications on its
233notification/event endpoint (NEEP). The beacon notifications are part of
234the event stream that is funneled into the API with
235/drivers/uwb/neh.c:uwb_rc_neh_grok()/ and delivered to the UWBD, the UWB
236daemon through a notification list.
237 238UWBD wakes up and scans the event list; finds a beacon and adds it to
239the BEACON CACHE (/uwb_beca/). If he receives a number of beacons from
240the same device, he considers it to be 'onair' and creates a new device
241[/drivers/uwb/lc-dev.c:uwbd_dev_onair()/]. Similarly, when no beacons
242are received in some time, the device is considered gone and wiped out
243[uwbd calls periodically /uwb/beacon.c:uwb_beca_purge()/ that will purge
244the beacon cache of dead devices].
245 246 247 Device lists
248 249All UWB devices are kept in the list of the struct bus_type uwb_bus.
250 251 252 Bandwidth allocation
253 254The UWB stack maintains a local copy of DRP availability through
255processing of incoming *DRP Availability Change* notifications. This
256local copy is currently used to present the current bandwidth
257availability to the user through the sysfs file
258/sys/class/uwb_rc/uwbx/bw_avail. In the future the bandwidth
259availability information will be used by the bandwidth reservation
260routines.
261 262The bandwidth reservation routines are in progress and are thus not
263present in the current release. When completed they will enable a user
264to initiate DRP reservation requests through interaction with sysfs. DRP
265reservation requests from remote UWB devices will also be handled. The
266bandwidth management done by the UWB stack will include callbacks to the
267higher layers will enable the higher layers to use the reservations upon
268completion. [Note: The bandwidth reservation work is in progress and
269subject to change.]
270 271 272 Wireless USB Host Controller drivers
273 274*WARNING* This section needs a lot of work!
275 276As explained above, there are three different types of HCs in the WUSB
277world: HWA-HC, DWA-HC and WHCI-HC.
278 279HWA-HC and DWA-HC share that they are Wire-Adapters (USB or WUSB
280connected controllers), and their transfer management system is almost
281identical. So is their notification delivery system.
282 283HWA-HC and WHCI-HC share that they are both WUSB host controllers, so
284they have to deal with WUSB device life cycle and maintenance, wireless
285root-hub
286 287HWA exposes a Host Controller interface (HWA-HC 0xe0/02/02). This has
288three endpoints (Notifications, Data Transfer In and Data Transfer
289Out--known as NEP, DTI and DTO in the code).
290 291We reserve UWB bandwidth for our Wireless USB Cluster, create a Cluster
292ID and tell the HC to use all that. Then we start it. This means the HC
293starts sending MMCs.
294 295 *
296 297 The MMCs are blocks of data defined somewhere in the WUSB1.0 spec
298 that define a stream in the UWB channel time allocated for sending
299 WUSB IEs (host to device commands/notifications) and Device
300 Notifications (device initiated to host). Each host defines a
301 unique Wireless USB cluster through MMCs. Devices can connect to a
302 single cluster at the time. The IEs are Information Elements, and
303 among them are the bandwidth allocations that tell each device
304 when can they transmit or receive.
305 306Now it all depends on external stimuli.
307 308*New device connection*
309 310A new device pops up, it scans the radio looking for MMCs that give out
311the existence of Wireless USB channels. Once one (or more) are found,
312selects which one to connect to. Sends a /DN_Connect/ (device
313notification connect) during the DNTS (Device Notification Time
314Slot--announced in the MMCs
315 316HC picks the /DN_Connect/ out (nep module sends to notif.c for delivery
317into /devconnect/). This process starts the authentication process for
318the device. First we allocate a /fake port/ and assign an
319unauthenticated address (128 to 255--what we really do is
3200x80 | fake_port_idx). We fiddle with the fake port status and /khubd/
321sees a new connection, so he moves on to enable the fake port with a reset.
322 323So now we are in the reset path -- we know we have a non-yet enumerated
324device with an unauthorized address; we ask user space to authenticate
325(FIXME: not yet done, similar to bluetooth pairing), then we do the key
326exchange (FIXME: not yet done) and issue a /set address 0/ to bring the
327device to the default state. Device is authenticated.
328 329From here, the USB stack takes control through the usb_hcd ops. khubd
330has seen the port status changes, as we have been toggling them. It will
331start enumerating and doing transfers through usb_hcd->urb_enqueue() to
332read descriptors and move our data.
333 334*Device life cycle and keep alives*
335 336Every time there is a successful transfer to/from a device, we update a
337per-device activity timestamp. If not, every now and then we check and
338if the activity timestamp gets old, we ping the device by sending it a
339Keep Alive IE; it responds with a /DN_Alive/ pong during the DNTS (this
340arrives to us as a notification through
341devconnect.c:wusb_handle_dn_alive(). If a device times out, we
342disconnect it from the system (cleaning up internal information and
343toggling the bits in the fake hub port, which kicks khubd into removing
344the rest of the stuff).
345 346This is done through devconnect:__wusb_check_devs(), which will scan the
347device list looking for whom needs refreshing.
348 349If the device wants to disconnect, it will either die (ugly) or send a
350/DN_Disconnect/ that will prompt a disconnection from the system.
351 352*Sending and receiving data*
353 354Data is sent and received through /Remote Pipes/ (rpipes). An rpipe is
355/aimed/ at an endpoint in a WUSB device. This is the same for HWAs and
356DWAs.
357 358Each HC has a number of rpipes and buffers that can be assigned to them;
359when doing a data transfer (xfer), first the rpipe has to be aimed and
360prepared (buffers assigned), then we can start queueing requests for
361data in or out.
362 363Data buffers have to be segmented out before sending--so we send first a
364header (segment request) and then if there is any data, a data buffer
365immediately after to the DTI interface (yep, even the request). If our
366buffer is bigger than the max segment size, then we just do multiple
367requests.
368 369[This sucks, because doing USB scatter gatter in Linux is resource
370intensive, if any...not that the current approach is not. It just has to
371be cleaned up a lot :)].
372 373If reading, we don't send data buffers, just the segment headers saying
374we want to read segments.
375 376When the xfer is executed, we receive a notification that says data is
377ready in the DTI endpoint (handled through
378xfer.c:wa_handle_notif_xfer()). In there we read from the DTI endpoint a
379descriptor that gives us the status of the transfer, its identification
380(given when we issued it) and the segment number. If it was a data read,
381we issue another URB to read into the destination buffer the chunk of
382data coming out of the remote endpoint. Done, wait for the next guy. The
383callbacks for the URBs issued from here are the ones that will declare
384the xfer complete at some point and call its callback.
385 386Seems simple, but the implementation is not trivial.
387 388 *
389 390 *WARNING* Old!!
391 392The main xfer descriptor, wa_xfer (equivalent to a URB) contains an
393array of segments, tallys on segments and buffers and callback
394information. Buried in there is a lot of URBs for executing the segments
395and buffer transfers.
396 397For OUT xfers, there is an array of segments, one URB for each, another
398one of buffer URB. When submitting, we submit URBs for segment request
3991, buffer 1, segment 2, buffer 2...etc. Then we wait on the DTI for xfer
400result data; when all the segments are complete, we call the callback to
401finalize the transfer.
402 403For IN xfers, we only issue URBs for the segments we want to read and
404then wait for the xfer result data.
405 406*URB mapping into xfers*
407 408This is done by hwahc_op_urb_[en|de]queue(). In enqueue() we aim an
409rpipe to the endpoint where we have to transmit, create a transfer
410context (wa_xfer) and submit it. When the xfer is done, our callback is
411called and we assign the status bits and release the xfer resources.
412 413In dequeue() we are basically cancelling/aborting the transfer. We issue
414a xfer abort request to the HC, cancel all the URBs we had submitted
415and not yet done and when all that is done, the xfer callback will be
416called--this will call the URB callback.
417 418 419 Glossary
420 421*DWA* -- Device Wire Adapter
422 423USB host, wired for downstream devices, upstream connects wirelessly
424with Wireless USB.
425 426*EVENT* -- Response to a command on the NEEP
427 428*HWA* -- Host Wire Adapter / USB dongle for UWB and Wireless USB
429 430*NEH* -- Notification/Event Handle
431 432Handle/file descriptor for receiving notifications or events. The WA
433code requires you to get one of this to listen for notifications or
434events on the NEEP.
435 436*NEEP* -- Notification/Event EndPoint
437 438Stuff related to the management of the first endpoint of a HWA USB
439dongle that is used to deliver an stream of events and notifications to
440the host.
441 442*NOTIFICATION* -- Message coming in the NEEP as response to something.
443 444*RC* -- Radio Control
445 446Design-overview.txt-1.8 (last edited 2006-11-04 12:22:24 by
447InakyPerezGonzalez)
448 449